Battery pack charging apparatus and method

ABSTRACT

A charging apparatus for charging a plurality of detachable battery packs includes a charging device for charging the plurality of battery packs one after another. A monitoring device is included to monitor attachment of a battery pack. A memory is included to switch from one of the battery data of a battery pack based upon a monitoring result. A switching device is included to switch from one of the battery packs to the next battery pack. A voltage detecting device is included to detect a voltage of the next battery pack before charging. A charging manner setting device is included to set any one of constant current charging and constant voltage charging in accordance with the detected voltage. A charge current detecting device is also included to detect a current during charging of the next battery pack.

BACKGROUND

[0001] 1. Field

[0002] This patent specification relates to a charging method capable ofcharging a plurality of secondary battery-packs (herein after refereedto as a battery pack) such as lithium ion batteries. In particular, itrelates to an optimal charging apparatus and method for charging spare(backup) battery packs used in an instrument body and mobile instrument,such as a mobile phone, a digital camera, etc.

[0003] 2. Discussion of the Background

[0004] Due to smallness of a power supply capacity of a chargingapparatus, a method of attaching and charging a plurality of batterypacks one after another in the charging apparatus has been practiced,and many patent applications thereabout has been filed. Even though theterm “a battery” is utilized in the below described literature, pluralbatteries serially arranged are generally used as a battery pack,because the voltage per cell of this type of secondary battery is small.

[0005] For example, Japanese Patent Application Laid Open No. 56-110446discloses a technology for efficiently charging normal batteries byskipping a battery that expresses abnormally lower voltage duringcharging. Japanese Patent Application Laid Open No. 56-166731 disclosesa technology for charging an inert battery in a similar manner to anormal battery by separately and sequentially charging a plurality ofbatteries one after another, using a charging control mechanism whencontrolling charging of each battery. Japanese Utility Model ApplicationPublication No. 4-24759 discloses a charging apparatus that charges aplurality of batteries one after another while detecting completion ofcharging of each battery. Such an apparatus detects attachment, andinitializes and proceeds to charge the uncharged batteries when theuncharged battery is attached. Japanese Patent Application Laid Open No.7-130399 refers to a technology capable of shortening a charging timeperiod by stopping charging when temperature of a battery in the courseof being charged exceeds a prescribed level, then charging the next one,and re-starting charging of the former battery when temperature of thenext battery exceeds a prescribed level.

[0006] According to these former two applications, charging of anadditional uncharged battery must be initiated by freshly attaching theuncharged battery after the entire batteries has been charged, becausedetection of the uncharged battery is impossible if the unchargedbattery is newly attached during charging. The charging apparatus ofJapanese Utility Model Application Publication No. 4-24759inconveniently recharges a charged battery which does not requireadditional charging, because the charging apparatus returns to aninitial condition and starts charging again restarting from the firstbattery when an uncharged battery is attached, even though the unchargedbattery is charged. Although a time period for charging the entirebatteries is advantageously shortened, the technology of Japanese PatentApplication Laid Open No. 7-130399 takes a long time period incompleting charging of the first battery in comparison with a case whencharging one by one. Further, since an uncharged battery is notdetected, charging can be started only by freshly attaching theuncharged battery after charging of the entire batteries has beencompleted, similar to the technology of Japanese Patent Application LaidOpen No. 56-166731 or the like. Further, a conventional chargingapparatus itself typically is bulky and costly, because a controlcircuit for charge control use in the conventional apparatus is entirelybuilt therein.

SUMMARY

[0007] Accordingly, an object of the present specification is to addressand resolve the above-noted and other problems and provide a new batterypack charging apparatus. The above and other objects are achievedaccording to the present specification by providing a novel battery packcharging apparatus that charges in turn a plurality of battery packswhich are attached to the apparatus. The novel battery pack chargingapparatus, according to one embodiment, includes a switching deviceoperative to switch the plurality of battery packs and select a batterypack to be charged, a charging circuit configured to charge the selectedbattery pack, a charging manner setting circuit operative to set any oneof constant current charging and constant voltage charging to beexecuted by the charging circuit during charging, a battery pack voltagedetecting circuit configured to detect a voltage of the selected batterypack, a charge current detecting circuit configured to detect a currentduring charging, a battery pack attachment detecting circuit configuredto detect an attachment condition of a battery pack, and a memoryconfigured to store detachment and attachment history data of a batterypack based on an attachment condition detected by the battery packattachment detecting circuit. A battery pack to be charged next andcharging manner therefor may be determined in accordance with thedetachment and attachment history data in the memory and the voltagedetected by the battery pack voltage detecting circuit, after currentcharging to a battery pack is completed.

[0008] In another embodiment, a preparatory charging process iscontinued for the battery pack until the detected voltage of the batterypack increases to a first voltage level after the detected voltage islower than the first voltage level. A constant current charging processis performed until the detected voltage of the battery pack grows up toa second voltage level when the detected voltage is higher than thefirst voltage level, and a constant voltage charging process isperformed until charge current flowing through a battery pack becomesless than a prescribed current after the voltage of the battery. packhas reached the second voltage level.

[0009] In yet another embodiment, when another battery pack has beenattached to the charging apparatus before current charging to thebattery pack is completed, the other battery pack is selected by theswitching device, and detachment and attachment history data related tothe other battery pack is read from the memory. When the other batterypack is additionally attached, charging thereto is performed by startingfrom a determination process for determining whether the detectedvoltage of the other battery pack is higher or lower than the firstvoltage level.

[0010] In yet another embodiment, when the other battery pack has beenalready attached before current charging to the battery pack has beencompleted and the detected voltage is lower than a third voltage level,constant current charging is performed thereto.

[0011] In yet another embodiment when the other battery pack has alreadybeen attached and the voltage is higher than the third voltage level,charging is omitted and it is detected if still another battery pack hasbeen attached.

[0012] In yet another embodiment, an attachment condition is alwaysmonitored by the battery pack attachment detecting circuit after currentcharging to the battery pack has been completed, and when anotherbattery pack has not been attached, the voltage of the battery pack towhich charging is completed is detected, and when the detected voltageis lower than the third voltage level, charging to the battery pack isstarted from the constant current charging process.

[0013] In yet another embodiment, at least one battery pack among theplural battery packs is built in a prescribed instrument body, and otherbattery packs are for backup use.

[0014] In yet another embodiment, the battery pack built in theprescribed instrument body is charged in preference to the other batterypacks.

[0015] In yet another embodiment, the charging manner setting circuit isincluded in the prescribed instrument body.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] A more complete appreciation of the invention claimed in theappended claims and many of the attendant advantages thereof may be morereadily understood from the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

[0017]FIG. 1 is a circuit diagram illustrating one example of a chargingapparatus according to the present invention;

[0018]FIG. 2 is a flowchart illustrating an operation of the chargingapparatus of FIG. 1;

[0019]FIG. 3 is a flowchart illustrating a sub routine for detecting anattachment condition of a battery pack; and

[0020]FIG. 4 is a circuit diagram illustrating another embodiment of thecharging apparatus according to the present specification.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] This application claims priority under 35 USC §119 to JapanesePatent Application No. 2002-030586 filed on Feb. 7, 2002, the entirecontents of which are incorporated by reference herein.

[0022] Referring now to the drawings, wherein like reference numeralsand marks designate identical or corresponding parts throughout severalviews, in particular in FIG. 1, an example of the present invention isillustrated. FIGS. 2 and 3 are flowcharts illustrating charging methodsaccording to the present invention. A charging apparatus 50 of FIG. 1illustrates an example using three battery packs P1 to P3. It should beunderstood by one skilled in the art after reading this specificationand the appended claims, however, that the apparatuses and methodologiesof this specification may be adapted for use with two or more batterypacks.

[0023] The charging apparatus 50 includes a charge control use FETsection 1 that performs switching control, a charge control circuit 2that controls charging, and switching devices 3 and 4. The chargingapparatus 50 itself is supplied with power source from an AC adapter.

[0024] Each of sources M1 to M3 of respective FETs (field effecttransistors) of switching control use FET1 is connected to a positivepotential of the AC adapter via a corresponding one of backflowprevention use diodes D1 to D3 and a corresponding one of resisters R1to R3. Further, each of the drains of the FETs is connected to acorresponding one of the plus terminals of the battery packs. Each ofthe gates of the FETs is connected to a charge FET control circuit 22included in the charge control circuit 2 via a corresponding one of theswitching devices 3 (S21 to S23). Minus terminals of the battery packsare mutually connected to each other at one side and connected to groundat the other side.

[0025] The charge control circuit 2 includes a charge current detectingcircuit 21 which detects a current during charging, a charge FET controlcircuit 22 which controls the switching control use FET1 so as toselectively perform constant current charging, constant voltagecharging, and preparative charging, and a battery pack voltage detectingcircuit 23 which detects a voltage of a battery pack attached. Alsoincluded are a battery pack attachment detecting circuit 24 whichdetects a battery pack attached to the charging apparatus 50, a controlcircuit 25 which controls the above mentioned circuits of the chargecontrol circuit 2 and switching devices 3 and 4, and a memory device 26which stores history data of battery pack attachment based upon a resultof monitoring of attachment of a battery pack. The monitoring may alwaysbe performed by the battery pack attachment detecting circuit 24 whilerespective connections performed by the switching device 4 areperiodically switched during charging to an arbitrary battery packattached to the charging apparatus 50.

[0026] These switching devices 3 and 4 are formed from mechanical orsemiconductor switches. Each of switches (S11 to S13) of the switchingdevice 3 is connected at one end thereof to a corresponding one ofconnection points between resisters (R1 to R3) and back flow preventiondiodes (D1 to D3) The other ends of the switches S11-S13 are mutuallyconnected to each other and further connected to the charge currentdetecting circuit 21. One end of each of the switches (S21 to S23) isconnected to a gate of a corresponding one of the FETs (M1 to M3) of thecharge control use FET1, and the other ends of the switches S21-S23 aremutually connected to each other and further connected to the charge FETcontrolling circuit 22 as mentioned above. One end of each of theswitches (S31 to S33) is connected to a plus terminal of a correspondingone of the battery packs, and the other ends of the switches S31-S33 aremutually connected to each other and further connected to the batterypack voltage detecting circuit 23.

[0027] The switches (S41 to S43) are connected on one end to terminals Twhich output prescribed signals when battery packs are attached to thecharging apparatus, and the other ends of the switches S41-S43 aremutually connected to each other and further connected to the batterypack attachment detecting circuit 24. The switches S11, S21 and S31included in the switching device 3 are simultaneously turned ON and OFF.Similarly, the switches S12, S22 and S32 are simultaneously turned ONand OFF, and the switches S13, S23 and S33 are simultaneously turned ONand OFF. Further, the switches S41 to S43 included in the switchingdevice 4 are independently operated from the switching device 3.

[0028] The control circuit 25 outputs a SW control signal “A” forcontrolling the switching device 3 and a SW control signal “B” forcontrolling the switching device 4. The SW control signal “A” switchescharge-receiving battery packs. Specifically, it switches the switchingdevices 3 from the currently charging battery pack to the next batterypack when charging of the current battery pack has been completed. TheSW control signal “B” checks a battery pack attached to the chargingapparatus, and turns the switches S41 to S43 ON one after anotherregardless of either a currently charging or charge standby condition. Atime period required for turning ON the switches S41 to S43 in turn isset to, for example several dozen ms, sufficiently shorter than theamount of time generally taken when a battery pack is detached from andattached to the charging apparatus 50.

[0029] A charging manner performed by the present charging apparatus 50is now described with reference to the flowcharts of FIGS. 2 and 3. Thecharging apparatus 50 starts charging in response to reception ofelectric power supply from the AC adapter. Initially, a battery pack P1which is to receive charging is selected by the switching device 4 andits voltage is detected (in step S2). The battery pack P1 is built in abody of any one of various instruments which can use the battery packand charging is started therefrom.

[0030] When the voltage of the battery pack P1 is less than a prescribedfirst voltage level (NO in step S3), preparatory charging is performed(in step S13). Such preparatory charging is performed with current lessthan that used in constant current charging performed thereafter. Avoltage therefor is set to about 2.5V per cell in a case of using aLithium battery. During preparatory charging, the charging current isrestricted to avoid a danger which is generally caused when a secondarybattery is in an over discharge condition and is suddenly charged withsuper power. Thus, a charging current for the preparatory charging isgenerally from around a few mA to around several dozen mA.

[0031] When the voltage of the battery pack P1 is either elevated by thepreparatory charging up to the first voltage level, or is larger thanthe first voltage level from the beginning, a constant current chargingis executed (YES in step S4). The constant current charging is performedwith a relatively large current set, in accordance with a capacity ofthe battery pack, so that the charging can be rapid. When the constantcurrent charging has progressed and the battery pack voltage reaches thesecond voltage level (instep S5), it is switched to constant voltagecharging (in step S6).

[0032] Since the lithium battery segregates metal lithium out, andaccordingly is dangerous when a charging voltage is high, the constantcurrent charging is generally switched to the constant voltage chargingwhen such charging has progressed up to a certain level, so as not toincrease the charging voltage. A voltage of the lithium battery at whichthe constant voltage charging is performed is set to around 4.2 volt percell. A charge current is monitored during the constant voltage charging(in step S7), and the constant voltage charging is completed when thecharge current becomes less than a prescribed current (in step S8).

[0033] It is checked, by analyzing the information in the memory 26,whether another battery pack is connected, after charging to the batterypack P1 is completed (in step S9). If another battery pack (P2) isconnected (YES in step S9), the switching device 3 switches to the otherbattery pack P2 (in step S10). Further, it is determined by analyzingthe information of the memory 26 whether the battery pack P2 is newlyattached (in step S11). If it is newly attached (YES in step S11) , theprocess returns to step S3, and it is determined if a voltage thereof iseither higher or lower than the first voltage level.

[0034] If the battery pack P2 is not newly attached (i.e., alreadyhaving been charged up to a voltage level 3) [NO in step S11], thevoltage thereof is checked (in step S12). If the voltage is more thanthe third voltage level (YES in step S12), charging to the battery packP2 is omitted, and the process returns to step S9, so that still anotherbattery pack attached can be searched for. If it is less than the thirdvoltage level (NO in step S12), the process returns to step S4 andconstant current charging is performed to the battery pack P2. The thirdvoltage level gives a reference for determining if the battery packdecreases in voltage, and accordingly, charging is necessary again dueto natural discharge. Thus, the third voltage is set to a voltage higherthan the second voltage level.

[0035] After the charging is completed (in step S8) and another batterypack attached does not exist any more (NO in step S9), the voltage ofthe charge completed battery pack is detected (instep S14). If thevoltage is greater than the third voltage level (YES in step S14), theprocess returns to step S9. Then, this loop is repeated until anotherbattery pack is attached. If it is less than the third voltage level (NOin step S14) the process returns to step S4, and constant currentcharging is performed to the formerly charged battery pack (i.e., P1 inthis case) (in step S4).

[0036] An operation of the switching device 4 is illustrated in FIG. 3.When the AC adapter is connected and electric power supply is input tothe charge controlling circuit (YES in step S14), in order to obtaininformation of battery packs attached to the charging apparatus 50, theswitching device 4 (S41 to S43) for battery packs P1, P2 and P3 isrepeatedly switched in this order (in step S16 to S18). A cycle ofrepetition is set sufficiently shorter than a time period during when abattery pack is detached and attached, such as on a scale of a few dozen“Ms” as mentioned above.

[0037]FIG. 4 illustrates another embodiment. In charging apparatus 51, aresistance, back flow prevention diode, and charge control use FET,which is provided per battery pack as illustrated in FIG. 1, is commonlyused by the battery packs. Specifically, a drain of the FET (M1) isconnected to any one of battery packs via the switching device 5 (S01 toS03). This circuit configuration can decrease a number of parts incomparison with that of FIG. 1. Since an operation of the circuit and acharging manner of the charging apparatus 51 are substantially the sameto those formerly described apparatus, these descriptions are omitted.

[0038] In another embodiment, at least one battery pack among the pluralbattery packs can be built in a prescribed instrument body, and otherbattery packs are for backup use. Further, a battery pack built in theprescribed instrument body can be charged in preference to the otherbattery packs.

[0039] In another embodiment, the charging manner setting circuit can beincluded in the prescribed instrument body.

[0040] The mechanisms and processes set forth in the present inventionmay be implemented using one or more conventional general-purposemicroprocessors and/or signal processors programmed according to theteachings of the present specification, as will be appreciated by thoseskilled in the relevant arts. Appropriate software coding can readily beprepared by skilled programmers based on the teachings of the presentdisclosure, as will also be apparent to those skilled in the relevantarts. However, as will be readily apparent to those skilled in the art,the apparatuses and methodologies of the present specification also maybe implemented by the preparation of application-specific integratedcircuits by interconnecting an appropriate network of conventionalcomponent circuits or by a combination thereof with one or moreconventional general purpose microprocessors and/or signal processorsprogrammed accordingly. The present invention thus also includes acomputer-based product which maybe hosted on a storage medium andinclude, but is not limited to, any type of disk including floppy disks,optical disks, CD-ROMs, magnet-optical disks, ROMs, RAMs, EPROMs,EEPROMs, flash memory, magnetic or optical cards, or any type of mediasuitable for storing electronic instructions.

[0041] In addition, it should be noted that the term “memory” is used ina broad manner to encompass RAMs, as well as any storage device to whichdata can be written, in which the data can be stored, and from which thedata can be read.

[0042] Numerous additional modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theapparatuses and methodologies of the present specification may bepracticed otherwise than as specifically described herein. For example,elements and/or features of different illustrative embodiments may becombined with each other and/or substituted for each other within thescope of the present disclosure and appended claims.

What is claimed is:
 1. A charging apparatus for charging a plurality ofdetachable battery packs, said charging apparatus comprising: a chargingdevice configured to charge the plurality of battery packs one afteranother; a monitoring device configured to monitor attachment of abattery pack to the charging apparatus; a memory configured to storeattachment history data based on monitoring of the battery pack by themonitoring device; a switching device operative to switch from one ofthe battery packs to a next one of the battery packs; a voltagedetecting device configured to detect a voltage of the next battery packbefore charging of the next battery pack commences; a charging mannersetting device operative to set any one of constant current charging andconstant voltage charging in accordance with the voltage detected by thevoltage detecting device; and a charge current detecting deviceconfigured to detect a current during charging of the next battery pack.2. The charging apparatus according to claim 1, wherein when thedetected voltage is lower than a first voltage level a preparatorycharging process is performed to the next battery pack until thedetected voltage increases to the first voltage level, when the detectedvoltage is higher than the first voltage level a constant currentcharging process is performed until the detected voltage increases to asecond voltage level, and after the voltage of the battery pack hasreached the second voltage level a constant voltage charging process isperformed until charge current flowing through the battery pack becomesless than a prescribed level.
 3. The charging apparatus according toclaim 1, wherein when the switching device switches to another batterypack, and said another battery pack is recognized as new based onattachment history data of said another battery pack from the memory,charging of said another battery pack is performed by starting from adetermination process for determining whether the detected voltage ofsaid another battery pack is higher or lower than a first voltage level.4. The charging apparatus according to claim 1, wherein when theswitching device switches to another battery pack, and said anotherbattery pack is determined to have already been attached based onattachment history data of said another battery pack from the memory,constant current charging of said another battery pack is performed ifthe detected voltage of the another battery pack is lower than a thirdvoltage level, said third voltage level being associated with a need ofcharging again due to natural discharge.
 5. The charging apparatusaccording to claim 4, wherein when the switching device switches toanother battery pack and said another battery pack is determined to havealready been attached based on attachment history data of said anotherbattery pack from the memory, and when a voltage of said another batterypack is higher than the third voltage level, charging is omitted and itis detected whether yet another battery pack has been attached.
 6. Thecharging apparatus according to claim 1, wherein the voltage of the nextbattery pack which has completed charging is detected if another batterypack has not been attached, and charging to the next battery pack isstarted from said constant current charging process if the detectedvoltage is lower than the third voltage level.
 7. The charging apparatusaccording to any one of claims 1 to 6, wherein at least one battery packamong the plurality of battery packs is built in a prescribed instrumentbody, and at least one other of the plurality of battery packs is forbackup use.
 8. The charging apparatus according to claim 7, wherein abattery pack built in the prescribed instrument body is charged inpreference to the other battery packs.
 9. The battery pack chargingapparatus according to any one of claims 1 to 6, wherein said chargingmanner setting device is included in the prescribed instrument body. 10.A method for charging a plurality of batteries, comprising the steps of:monitoring battery pack attachment to a charging apparatus; storingattachment history data of a battery pack based on a monitoring result;switching battery packs from one battery pack of which charging iscomplete to an uncharged battery pack; detecting a voltage of theuncharged battery pack; determining a charging manner based on thedetected voltage; setting a charging method to any one of constantcurrent charging and constant voltage charging in accordance with thedetected voltage; charging the uncharged battery pack by using the setcharging method; and detecting a current during charging of theuncharged battery pack and stopping charging when the detected currentis below a predetermined current level.